Disease Severity Values and P-Days

Each year we operate four automated weather stations, located in Hancock, Grand Marsh, Plover, and Antigo. Data from these stations is used to run predictive disease severity models to give growers the information they need to mitigate disease risk in potato production. Current P-days and DSVs can be accessed on this page.

DSVs: Late blight risk can be modeled using disease severity values (DSVs). First, select your nearest weather station. On the chart shown, highlight the date of your last spray and note the cumulative DSVs at that point. Then subtract that number from the most recent cumulative DSV value to get the accumulated DSVs since your last spray. When this value exceeds 18, late blight management action is recommended. You can download each chart by clicking on the menu button on the upper right corner. Visit VDIFN and select the Late Blight model for a statewide map of late blight risk.

P-Days: Early blight risk is elevated after 300 P-Days (physiological days) have accumulated after crop emergence. Early blight management actions are recommended beyond that point. You may need to subtract accumulated P-Days from prior to your specific crop emergence date from the weather station report. Visit VDIFN and select the Early Blight model for a statewide map of P-Days and early blight risk.

Data access and station locations: See links below charts.

Known issues: The Hancock station has been damaged by rodents and the air temperature and relative humidity sensors are offline.




The Antigo station features a pyranometer that measures solar insolation. View this data in the spreadsheets linked below.

Data access: